Enamine

An enamine contains an amino nitrogen bonded to an alkene carbon. Delocalization between the nitrogen lone pair and the alkene makes its carbon nucleophilic; carbon alkylation can give an iminium ion that hydrolyses to a carbonyl compound.

Enamine alkylation forms a carbon–carbon chemical bond by using an enamine as a carbon-centred nucleophile. The nitrogen substituent donates electron density into the adjacent carbon–carbon double bond, enabling attack on an appropriate alkyl electrophile.

In the familiar carbonyl-functionalization sequence, a ketone or aldehyde first forms an enamine with an amine. Carbon alkylation gives an iminium-containing intermediate, and hydrolysis restores the carbonyl group. The net result can be substitution next to the original carbonyl carbon. Regioselectivity, competing nitrogen alkylation and substrate compatibility matter; the net product formula does not specify a universally selective reaction.

An iminium intermediate can lose a proton at either adjacent carbon, generating different enamine double-bond positions. Reaction selectivity can depend on which regioisomer is populated.